Anti-receptor and growth blocking antibodies to the vitamin B12 /transcobalamin II receptor and binding sites

ABSTRACT

There is disclosed anti-receptor and growth blocking agents to the vitamin B 12  /transcobalamin II receptor and binding sites. The anti-receptor and growth blocking agents antagonize or modulate the vitamin B 12  /transcobalamin II receptor or binding sites, causing cellular depletion of vitamin B 12 , thus preventing or inhibiting cell division or causing apoptosis. Anti-receptor and growth blocking agents of the present invention include proteins (such as antibodies and antibody derivatives), peptides and small organic molecules. In a preferred embodiment, the anti-receptor agent is an antibody to the vitamin B 12  /transcobalamin II receptor.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a continuation-in-part of pending U.S. patent application Ser. No. 07/880,540, filed May 8, 1992 now abandoned.

TECHNICAL FIELD

The present invention generally relates to anti-receptor or growth blocking agents directed to vitamin B₁₂ /transcobalamin II receptors or binding sites, and more specifically, to agents which can cause the cellular depletion of vitamin B₁₂ by antagonizing or modulating the vitamin B₁₂ /transcobalamin II receptors or binding sites, thereby inhibiting cell division or resulting in cellular apoptosis.

BACKGROUND OF THE INVENTION

Experimental in vitro data, pre-clinical animal models, and patient studies have demonstrated the requirement of proliferating normal and neoplastic cells for vitamin B₁₂. This nutrient is a co-factor for enzymes necessary in cell division, as well as cellular metabolism. Insufficient vitamin B₁₂ had several ramifications. Cellular division is held in abeyance and apoptosis may result. The nutrient is generally derived from dietary intake and is transported throughout the body complexed to transport proteins. The complex of transport protein and vitamin B₁₂ is recognized by a cellular receptor which internalizes the complex and releases the vitamin intracellularly. The overall process has been recently reviewed (GUT 31:59, 1991). Vitamin B₁₂ is taken in through the diet. Binding proteins in the saliva (R-binder) and gut (intrinsic factor-(IF)) complex B₁₂ after release from endogenous binding proteins by action of enzymes and low pH in the stomach. B₁₂ is transferred across the intestinal epithelium in a receptor specific fashion to transcobalamin II (TcII). The vitamin B₁₂ /transcobalamin II complex is then transported throughout the body and recognized by receptors present on dividing cells, internalized and released within the cell where it is utilized by certain enzymes as a co-factor.

The high affinity receptor in dividing tissues or cells responsible for internalization of B₁₂ recognizes transcobalamin II complexed with vitamin B₁₂. The B₁₂ /TcII receptor recognizes only the vitamin B₁₂ /TcII complex and not the serum transport protein or the vitamin alone. The receptor is undetectable on non-dividing cells; the mechanism for supplying non-dividing cells with vitamin B₁₂ is poorly understood. However, it is known that more vitamin B₁₂ is required during cell division than during metabolism, and that the B₁₂ /TcII receptor is the only high affinity means for cellular uptake of vitamin B₁₂ during cell division. When stimulated to divide, cells demonstrate transient expression of this receptor leading to B₁₂ uptake which precedes actual DNA synthesis (J. Lab. Clin. Med 103:70, 1984). Vitamin B₁₂ receptor levels may be measured by binding of ⁵⁷ Co-vitamin B12 complexed to transcobalamin II (present in serum) on replicate cultures grown in chemically defined medium without serum. No receptor mediated uptake occurs in the absence of carrier protein.

Dividing cells, induced to differentiate, lose receptor expression and no longer take up vitamin B₁₂. More importantly, leukemic cells, deprived of vitamin B₁₂, will stop dividing and die (Acta Haemat. 81:61, 1989). In a typical experiment, leukemic cell cultures were deprived of serum for 3 days, and then supplemented either with serum (a source of B₁₂) or a non-metabolizable analogue of B₁₂ and cultured up to five days. Cell cultures supplemented with vitamin B₁₂ continued to grow whereas those deprived of the active nutrient stopped growing and died.

Based on these observations, it has been suggested that whole body deprivation of vitamin B₁₂ may be useful in the treatment of cancer or other disorders characterized by uncontrolled growth of cells. Moreover, because of the critical role played by vitamin B₁₂ -containing enzymes in cell division, it is believed that B₁₂ deprivation may be used in combination with chemotherapeutic drugs which inhibit cellular replication. For example, when vitamin B₁₂ depletion was combined with methotrexate, the two modalities together were more efficient in depleting folate levels in leukemic cells than either alone (FASEB J. 4:1450, 1990; Arch. Biochem. Biophys. 270:729, 1989; Leukemia Research 15:165, 1991). Folates are precursors in the production of DNA and proteins. In typical experiments, cultures of leukemic cells were exposed to nitrous oxide for several hours to convert the active form of endogenous B₁₂ to an inactive form. Replicate cultures were then left without further treatment, or additionally treated with methotrexate. Cellular folate levels were measured three days later. Cells treated with the combination (i.e., both methotrexate and inactive B₁₂) showed a more striking decrease in cellular folate levels than with either of the two approaches alone. This combination also results in a higher cell kill in vitro. When this approach was applied to the treatment of highly aggressive leukemia/lymphoma in animal models (Am. J. Haematol. 34:128,1990; Anticancer Res. 6:737, 1986; Cancer Chemother. Pharmacol. 17:114, 1986; Br. J. Cancer 50:793, 1984), additive or synergy of anti-tumor action was observed, resulting in prolonged remissions and cures. The following Table 1 summarizes the observed additive or synergistic results:

                  TABLE 1                                                          ______________________________________                                         Vitamin B.sub.12 Depletion (Nitrous Oxide) in Combination Therapy                            Drugs Used in                                                                  Combination with                                                                               Therapeutic                                      Study         Vitamin B.sub.12 Depletion                                                                     Results                                          ______________________________________                                         Myelocytic leukemia/rats                                                                     cycloleucine    additive                                                       5-FU            additive                                                       methotrexate    synergistic                                      Acute leukemia/rats                                                                          5-FU            additive                                         Acute leukemia/rats                                                                          methotrexate    synergistic                                      Acute leukemia/rats                                                                          cycloleucine    synergistic                                      ______________________________________                                    

A key finding in the experiments described above was that short-term (hours to days), whole body depletion of vitamin B₁₂ can act synergistically with chemotherapeutic drugs (such as methotrexate and 5-FU) to inhibit tumor growth and treat animals with leukemia/lymphoma. Despite synergistic anti-tumor activity, there was no toxicity attributable to the short-term vitamin B₁₂ depletion for proliferating normal cells. This combination therapy was demonstrated in multiple animal models. Observations in patients have indicated that long-term (months to years) vitamin B₁₂ depletion is required to produce significant normal tissue toxicity. Even in those cases, subsequent infusion of B₁₂ can readily reverse symptomology (Br. J. Cancer 5:810, 1989).

Because of the promise of this therapeutic approach, various methods have been sought to efficiently and controllably perform a temporary depletion of vitamin B₁₂. Such methods, however, affect all of the body's stores of vitamin B₁₂. They include dietary restriction, high doses of vitamin B₁₂ analogues (non-metabolizable-competitive antagonists which act as enzyme inhibitors), and nitrous oxide (transformation of B₁₂ to inactivate form). These different methods have been used in culture systems and in animals to deplete vitamin B₁₂. The most efficient and the most utilized method has been the inhalation of nitrous oxide (laughing gas). Animals are maintained typically under an atmosphere of 50% to 70% of nitrous oxide for periods from a few hours to a few days, causing the conversion of endogenous B₁₂ into an inactive form. This methodology has been utilized in combination with drugs for therapy of leukemia/lymphoma. A further method for vitamin B₁₂ depletion involves infusion of a non-metabolizable analog of B₁₂ which essentially dilutes out the active form. This form of therapy is not specific for dividing cells but affects liver dependent metabolic processes. Another approach includes restricting the dietary intake of vitamin B₁₂. This method, however, requires very long periods of dietary restriction and is offset by hepatic storage of vitamin B₁₂. All of these methods suffer from problems of specificity, since they affect both B₁₂ -dependent growth as well as basal metabolism, and therefore are not particularly suited to the development of anti-proliferative pharmaceutical products.

Accordingly, there is a need in the art for agents which will cause the cellular depletion of vitamin B₁₂, and which selectively affect dividing cells. The present invention fulfills this need, and provides further related advantages.

SUMMARY OF THE INVENTION

The present invention discloses anti-receptor or growth blocking agents which antagonize or modulate the vitamin B₁₂ /transcobalamin II receptor ("B₁₂ /TcII receptor") or binding sites on the B₁₂ /TcII complex ("binding site"). Such agents cause cellular depletion of vitamin B₁₂ by interfering with receptor or binding site, thus preventing or inhibiting cell division and ultimately resulting in cellular apoptosis. Anti-receptor or growth blocking agents which antagonize (e.g., block) the B₁₂ /TcII receptor or function by competitively binding to the receptor or binding site, thereby preventing cellular uptake of vitamin B₁₂. Alternatively, the antagonists may sterically hinder recognition of the complex by the receptor or interfere with the binding site by binding sufficiently near the receptor or binding site, and thus prevent cellular uptake of vitamin B₁₂.

Anti-receptor or growth blocking agents of the present invention which modulate the vitamin B₁₂ /transcobalamin II receptor or binding sites, bind to the receptor or binding site and cause the removal or clearing of the receptor or for a period of time, and thus inhibit cellular uptake of vitamin B₁₂. Anti-receptor or growth blocking agents of the present invention include proteins (e.g., antibodies and antibody derivatives), peptides and small organic molecules that can antagonize or modulate the vitamin B₁₂ /transcobalamin II receptor and cause the cellular depletion of vitamin B₁₂, thereby inhibiting cell division of normal or neoplastic cells.

In one embodiment of the present invention, an anti-receptor agent to the vitamin B₁₂ /transcobalamin II receptor is disclosed. This agent is capable of competitively antagonizing or modulating the receptor to prevent cellular uptake of vitamin B₁₂. In a preferred embodiment, the anti-receptor agent is an antibody (or derivative thereof) to the vitamin B₁₂ /transcobalamin II receptor.

In another embodiment of the present invention, growth blocking agents are directed to the TcII binding site. (FIG. 4, type 1). The growth blocking agent of this embodiment affects B₁₂ uptake, since B₁₂ can not enter the cell in effective amounts without binding to TcII.

In another embodiment of the present invention, growth blocking agents are directed to the holo-TcII binding site. (FIG. 4, type 2). The growth blocking agents of this embodiment affects B₁₂ uptake by preventing the complex from binding to a cell surface receptor.

In another embodiment of the present invention, growth blocking agents are directed to the apo-TcII binding site. (FIG. 4, type 1) . The growth blocking agents of this embodiment affects B₁₂ uptake by preventing the TcII/B₁₂ complex from binding a cell surface receptor and/or preventing B₁₂ from binding TcII.

In another embodiment of the present invention, growth blocking agents are directed to clearing sites. The growth blocking agents for this embodiment are capable of redirecting TcII or the TcII/vitamin B₁₂ complex to the reticulo-endothelial organs, such as the liver and spleen, thus affecting B₁₂ uptake

In a further embodiment, the present invention discloses a method for inhibiting cell division in warm-blooded animals or biological preparations by administering to the animal an anti-receptor agent or a growth blocking agent, wherein the agent is capable of antagonizing or modulating the receptor or binding site to prevent or inhibit cellular uptake of vitamin B₁₂ for the treatment of neoplastic disorders and other disorders characterized by uncontrolled growth of normal cells.

In yet a further embodiment, a method is disclosed for preventing or inhibiting cellular uptake of vitamin B₁₂ in warm-blooded animals or biological preparations by administering to the animal an anti-receptor agent or a growth blocking agent, wherein the agent is capable of antagonizing or modulating the receptor or binding site.

DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates the development of vitamin B₁₂ transcobalamin II receptor antibodies through the production of murine monoclonal antibodies to the receptor using immunogens consisting of a solid phase, affinity sorbent for the receptor to elicit antibodies, followed by hybridoma generation and screening using both binding and functional assays.

FIG. 2 illustrates the administration of vitamin B₁₂ anti-receptor antibodies (i.e., infusions every 2 to 3 days) to maintain serum concentrations above the requisite level (indicated by tri-partite line) for complete or near complete receptor blockade. The requisite concentration is determined by the amount of antibody required to block ≧90% of vitamin B₁₂ uptake into cultured leukemic cells (K562) as assessed by functional assays.

FIG. 3 illustrates assessment of vitamin B₁₂ /transcobalamin II receptor modulation by vitamin B₁₂ anti-receptor antibodies. 100 ng/ml of antibody is incubated with 1 million Raji Burkitt lymphoma cells. Half of the cells are held at 4.0° C. and half transferred to 37° C. after washing. Thirty minutes to 2 hours later, samples are assessed for residual mouse Ig bound to cells by flow cytometry (MFI=mean fluorescence intensity) of all cells.

FIG. 4 illustrates some of the binding types utilized in the present invention.

FIG. 5 illustrates the screening assay used to identify monoclonal antibodies that recognize human TcII and prevent binding of vitamin B₁₂.

FIG. 6 illustrates screening of monoclonal antibodies for abilities ability to inhibit uptake of ⁵⁷ Co labelled vitamin B₁₂.

FIG. 7 illustrates the selectivity of monoclonal for holo-TcII assessed by immunoprecipitation.

FIG. 8 illustrates a two-site ELISA assay for anti-TcII monoclonal antibodies. Transcobalamin II was detected in human serum with combinations of anti-TcII monoclonal antibodies. ELISA plates were coated with 10 ug/ml of monoclonal antibodies, 50 ul of human serum was added to blocked plates and bound TcII detected with biotinylated secondary monoclonal antibodies.

DETAILED DESCRIPTION OF THE INVENTION

The present invention discloses anti-receptor agents to the vitamin B₁₂ /transcobalamin II ("B₁₂ /TcII") receptor and growth blocking agents directed to binding sites on the vitamin B₁₂ /transcobalamin II complex ("B₁₂ /TcII complex"). Within the context of the present invention, "anti-receptor agents" or "growth blocking agents" cause cellular depletion of vitamin B₁₂, ultimately resulting in cellular apoptosis, by acting as competitive antagonists or as modulating agents to vitamin B₁₂ /TcII receptors or binding sites on the B₁₂ /TcII complex. The anti-receptor and growth blocking agents of the present invention recognize certain functional and nonfunctional binding sites on TcII and the receptor, as described below, and modulate, antagonize, inhibit or prevent vitamin B₁₂ uptake by the cell. Since dividing cells require larger quantities of vitamin B₁₂, this results in the inhibition of cellular proliferation and, ultimately, apoptosis.

Competitive antagonists are agents which competitively bind to (or sterically hinder) the B₁₂ /TcII receptor or binding sites, thereby preventing or inhibiting cellular uptake of vitamin B₁₂. Modulating agents bind to the B₁₂ /TcII receptor or binding sites, and result in the clearing or removal of the receptor or the B₁₂ /TcII complex for a period of time (generally hours), assuming the modulating agent is no longer present. Anti-receptor and growth blocking agents of the present invention include proteins (such as antibodies), peptides and small organic compounds.

In another aspect, the present invention is directed to novel methods for depletion of cellular vitamin B₁₂ in warm-blooded animals or biological preparations by administration of an anti-receptor antibody or growth blocking agent, for example, administering to a warm-blooded animal an anti-receptor or growth blocking antibody to the B₁₂ /TcII complex, wherein the antibody competitively antagonizes or modulates the receptor or binding site to prevent or inhibit cellular uptake of vitamin B₁₂. Due to the low expression of the B₁₂ /TcII receptor (e.g., only a few thousand per cell) and the need to generate functional antibodies that elicit a biological response (e.g., cause cellular depletion of vitamin B₁₂ and perhaps apoptosis), novel methods of immunization are described herein for eliciting functional antibodies (e.g., combining affinity enrichment of the receptor together with the use of solid phase immunogens to enhance the response to these weakly immunogenic and poorly expressed antigens). Only a portion of these anti-receptor antibodies function as antagonists or to modulate cellular receptors or binding sites. Appropriate antibodies may be identified by bioassays as illustrated below and in FIG. 1.

In the context of the present invention, the term "anti-receptor agent" or "growth blocking agent" refers to compounds or compositions such as proteins, peptides, and small organic compounds which act by binding to binding sites on B₁₂ /TcII complex or the cell surface and result in the cellular depletion of vitamin B₁₂.

The term "binding site" refers to a functional or nonfunctional binding site on TcII or the B₁₂ /TcII complex which, when bound by a growth blocking agent of the present invention, results in occlusion, causes conformational changes which would occlude, or otherwise hinders, i.e., sterically, or modulates the functional binding site on TcII or the B₁₂ /TcII complex.

The term "TcII binding site," refers to a binding site on TcII which allows binding between TcII and vitamin B₁₂ (FIG. 4, type 1). The growth blocking agent of this embodiment affects B₁₂ uptake since B₁₂ can not enter the cell in effective amounts without binding to TcII.

The term "holo-TcII binding site" refers to a binding site on the TcII/vitamin B₁₂ complex which allows the complex to bind to a cell surface receptor (FIG. 4, type 2). The growth blocking agent of this embodiment affects B₁₂ uptake by preventing the complex from binding to a cell surface.

The term "apo-TcII binding site" (FIG. 4, type 1) refers the binding site on TcII, before binding to the vitamin B₁₂, which binds the TcII/vitamin B₁₂ complex to the cell surface. The growth blocking agent of this embodiment affects B₁₂ uptake by preventing the TcII/B₁₂ complex from binding a cell surface receptor and/or preventing B₁₂ from binding TcII.

The term "clearing sites" refers to any binding sites on TcII or the TcII/vitamin B₁₂ complex to which a growth blocking agents are capable of binding. The growth blocking agent for this embodiment is capable of redirecting TcII or the TcII/vitamin B₁₂ complex to the reticulo-endothelial organs, such as the liver and spleen, thus affecting B₁₂ uptake.

The term "TcII/vitamin B₁₂ receptor" refers to a receptor for TcII/vitamin B₁₂ complex to the cell membrane or surface. (FIG. 4, type 3).

The term "biological preparation" refers to any animal cell or tissue ex vivo. Suitable preparations include, by way of example, HepG2 cells, COS cells, 293 cells, K562 cells, and ATT20 cells.

In one aspect of the present invention, the anti-binding or growth blocking agent is an antibody. In the context of the present invention, the term "antibody" includes both monoclonal and polyclonal antibodies and further includes an intact molecule, a fragment thereof, or a functional equivalent thereof.

Anti-receptor and growth blocking antibodies of the present invention fall into several functional and specificity categories and have different pharmaceutical applications. Suitable anti-receptor antibodies to the B₁₂ /TcII receptor include those which (1) bind but do not produce a biological response; (2) cross-link, modulate and clear the surface of receptors and, if the concentration of modulating antibody is maintained in the patient's circulation at sufficient levels, modulate any newly synthesized receptor when it is re-expressed (IgM antibodies typically are the most efficient modulating agents); and (3) function as competitive antagonists for vitamin B₁₂ binding.

Suitable growth blocking antibodies include any antibody which is capable of binding to, or otherwise occluding, a binding site or any antibody which is capable of binding to a binding site and clearing TcII or the TcII/vitamin B₁₂ complex from circulation. Each of these types of antibodies may be distinguished by specific binding or functional assays in a series of screens, beginning with primary screens using initial hybridoma cultures, through secondary screens of clones, and finally to more labor intensive assays of final, stably secreting clones. (See Examples 1, 2, 8-12 and FIG. 1.) For example, a suitable growth blocking antibody to a chosen binding site may be selected by any one of several means known in the art, including the use of functional binding assays described in detail in Sambrook et at., Antibodies: A Laboratory Manual, Cold Spring Harbor Laboratory, 1989 and the Examples below. Briefly, antibodies are incubated with a pre-formed complex of (⁵⁷ Co) Vitamin B₁₂ /TcII then exposed to a suitable B₁₂ receptor bearing cells including, by way of example, K562 cells (ATCC accession no. CCL-243). Uptake is then measured using any suitable means of detecting the radiolabeled antibodies (see, Example 10).

In a preferred embodiment, murine antibodies are generated and used to demonstrate the comparability of antibody mediated depletion to nitrous oxide conversion of vitamin B₁₂, and causing apoptosis or death of tumor cells in a biological preparation. The pharmaceutical application of murine antibodies, however, is limited by the potential for anti-murine antiglobulin responses in patients (i.e., immunogenicity). Thus, murine antibodies require genetic manipulation for their conversion to human-mouse chimeras. Numerous methods exist for conversion of murine antibodies to chimeras in which the heavy and light chain constant regions are substituted with human versions or in which all but the CDRs (complementary determining regions) are substituted with their human equivalents. (See Biochem. J. 281:317, 1992; Proc. Nat. Acad. Sci. USA 86:10029, 1989; Methods Enzymol. 178:515, 1989; Cancer Res. 51:181, 1991; Biotechniques 7:360, 1989; J. Immunol. 143:3589, 1989; Int. J. Cancer 44:424, 1989; Proc. Nat. Acad. Sci. USA 86:3833, 1989).

In another preferred embodiment of the present invention, the serum half-life of the growth blocking or anti-receptor agents is adjusted for the particular application. For certain applications it may be valuable to increase the serum half-life using any one of several means including selecting heavy chain constant regions which will impart long serum half-life. Particularly, when using a competitive antagonist, the affinity and the length of exposure to target cells is of critical importance to efficacy. Optimal cell depletion is accomplished by blocking receptors or binding sites for several hours to several days. Suitable antibodies may be selected by any one of several means including radiolabelling IgG, injecting it into a warm-blooded animal, and drawing blood samples over a period of time and ascertaining the level of IgG. Human IgG antibodies have half-lives varying from 24 hours to several days. Chimeric IgG antibodies need to be assessed for this property individually. Human IgM have half lives that can exceed several days and, despite their slow rate of penetrance into tissues, may be the most suited to applications where receptor antagonism or modulation must be maintained for prolonged periods. (See Biochem. J. 281:317, 1992; Proc. Nat. Acad. Sci. USA 86:10029, 1989; Methods Enzymol. 178:515, 1989; Cancer Res. 51:181, 1991; Biotechniques 7:360, 1989; J. Immunol. 143:3589, 1989; Int. J. Cancer 44:424, 1989; Proc. Nat. Acad Sci. USA 86:3833, 1989). A longer serum half-life may be engineered using only one of several means, including selecting for IgG4 and IgG2, human IgM heavy chains or screening multiple IgG heavy chain allotypes for these longest half-life using any one of several means.

Completely human monoclonal antibodies can also be created by in vitro immunization procedures, employing the specific sorbents used in murine hybridoma generation. See Example 1 below and FIG. 1. Furthermore, a variety of techniques exist for in vitro immunization and human antibody generation (J. Immunol. Methods 145:71, 1991; Hybridoma 9:81, 1990; Proc. Nat. Acad Sci. USA 85:3995, 1988; Immunol. Lett. 17:29, 1988; BBRC 148:941, 1987; Immunol. Lett. 16:75, 1987; Tissue Antigens 30:25, 1987). See also U.S. Pat. No. 4,879,225 (herein incorporated by reference in its entirety).

In another aspect of the present invention, genetic engineering techniques can be used to produce various antibody derivatives including fragments, peptides, or organic molecule mimetics, as well as a variety of antibodies modified with regard to affinity or effector function. Preferably, murine antibodies are used. All these various antibody derivatives can be produced from an antibody to the B₁₂ /TcII receptor or binding site. Essentially, one can consider such an antibody as containing, within its antigen combining site, the information necessary to combine with its target and elicit a biologic response. This information can be put into the context of molecules of different size and different forms, and are collectively referred to herein as "antibody derivatives".

The aforementioned chimeric antibodies (which are typically whole IgG) can be engineered by a number of different approaches but essentially seek to replace murine constant regions with those of human origin. Alternatively, the CDRs (i.e., the specific regions interacting with the antigen) can be isolated from the antigen combining site and then engrafted into a framework of human variable, as well as constant, regions. This latter type of antibody should be less immunogenic than chimeric antibodies in which only constant regions are replaced. More recently, efforts have been initiated in identifying the most probable residues within a murine antibody structure that elicits antiglobulin or HAMA responses. Essentially, these may be hydrophilic residues that are in contact with solvent and can be identified and replaced by mutagenesis of antibody genes.

For certain applications it may be favorable to shorten serum half-life in order to provide better penetration into tissues or to clear background blood levels. Such applications include bone marrow protection from chemotherapeutic drugs or radiation. In this case, it may be appropriate to adjust the biological half-life of the antibody to induce a short term anti-proliferative block of bone marrow stem cells, timed to coincide with administration of chemotherapeutic drugs or radiation. Following cessation of treatment with the toxic therapy, cell proliferation would be restored as the growth blocking or anti-receptor agent was eliminated from the body.

In yet another aspect of the present invention, a whole antibody is engineered into one of the various fragments as identified in Table 2. The most common antibody fragments produced by genetic engineering are the Fab or Fv fragments. Fab fragments can be created by enzymatic digestion of whole IgG, but this usually entails a significant loss in product, as well as inconsistencies in the final antibody form. Thus, genetically engineered Fab is believed to be a more consistent product, and can be produced in gram-per-liter quantities in bacterial expression systems. An important step in producing such engineered fragments is to isolate the regions of the antibody involved in antigen binding (i.e., the CDRs) and place them within the context of human framework. Essentially, Fv is created in a similar manner to Fab, except that the Ch1 and Vh domains are not cloned along with CDR regions. This gives rise to a smaller fragment that requires peptide linkers to join the heavy and light chain components. Moreover, it is believed that certain heavy chain domains can combine with target antigens without the participation of a light chain domain. This is likely to be confined to rather primitive antibodies and antigen-binding specificities. The smallest antibody fragment consists of peptides derived from the information in the CDR, but retain the ability to bind to target structures. Since the affinity of these antibody fragments (as well as Fab and Fv) must be maintained with cloning, bivalent antibody fragments may be created, as well as ones in which mutagenesis and selection has been applied to select a higher affinity version. Preferably, the antibody affinity to its target is in the range of about 10⁻⁷ to 10⁻¹⁰ M, and, even more preferably, affinity is greater than 10⁻⁹ M.

                                      TABLE 2                                      __________________________________________________________________________     Genetically Engineered Antibody Derivatives                                    Which May Function As Receptor Antagonists                                     Derivative   References                                                        __________________________________________________________________________     Antibody Fragments                                                             CH.sub.2 deletion                                                                           Mueller et al., PNAS 87:5702-5, 1990; Kashmiri, 3rd IBC                        Conference on Antibody Engineering, May 14, 1992                  CH.sub.3 deletion                                                                           Kashmiri, 3rd IBC Conference on Antibody Engineering,                          May 14, 1992                                                      Fab          Ward et al., Nature 341:544-6, 1989; Chiswell & McCafferty,                    TIBTech 10:80-84, 1992; Carter et al., Biotechnology                           10:163-                                                                        167, 1988; Better et al., Science 240:1041-43, 1988               Fv           Huston et al., Methods in Enzymology 203:46-88, 1991;                          Colcher et al., JNCI 82:1191-97, 1990; Skerra & Pluckthun,                     Science 240:10-38, 1988; Whitlow & Filpula, Methods: A                         Companion to Methods in Enzymology 2:97-105, 1991                 Heavy chain domain                                                                          Ward et al., Nature 341:484-5, 1989                               MRU/Peptide mimetics                                                                        Williams et al., PNAS 86:5537-41, 1989; Taub et al., J.                        Biol.                                                                          Chem. 264:259-65, 1989                                            Chimeric Antibodies                                                            Chimeric (mouse V region/                                                                   R. F. Kelley, 3rd IBC Conference on Antibody Engineering,         human constant regions)                                                                     May 14, 1992; Morrison & Oi, Adv. Immunol. 44:65-92, 1989;                     Larrick & Fry, Hybridoma 2:172-89, 1991                           Primatized (mouse V region/                                                                 R. A. Newman, 3rd IBC Conference on Antibody Engineering,         primate constant regions)                                                                   May 14, 1992                                                      CDR grafted (mouse CDR,                                                                     Chiswell & McCafferty, TIBTech 10:80-84, 1992; T. Rees, 3rd       human constant and frame-                                                                   IBC Conference on Antibody Engineering, May 14, 1992;             work regions)                                                                               C. Queen, 3rd IBC Conference on Antibody Engineering,                          May 14, 1992; Junghans et al.; Cancer Res. 50:1495-1502,                       1990; Tempest et al., Biotechnology 9:266-71, 1991; Jones                      et                                                                             al., Nature 321:522-5, 1986                                       Hydrophillic residue                                                                        T. Rees, 3rd IBC Conference on Antibody Engineering,              substitution May 14, 1992                                                      Modified Antibodies                                                            Antigen Affinity                                                                            Ashkenazi et al., PNAS 87:7150-4, 1990; Clarkson et al.,                       Nature 352:624-628, 1991; Queen et al., PNAS 86:10029-33,                      1989; Tempest et al., Bio/Technology 9:266-72, 1991;                           Chiswell & McCafferty, TIBTech 10:80-84, 1992; Foote &                         Winter, J. Mol. Biol. 224:487-99, 1992                            Effector Functions                                                                          Wawrzynczak et al., Mol. Immunol. 29:213-20, 1992;                             Wawrzynczak et al., Mol. Immunol. 29:221-7, 1992; Lund et                      al., J. Immunol. 147:2657-62, 1991; Duncan et al., Nature                      332:563-4, 1988; Duncan & Winter, Nature 332:738-40, 1988         Bi-specific  Berg et al., PNAS 88:4723-7, 1991; D. Segal, Chem. Immunol.                    47:179-213, 1989; Rodriques et al., Int. J. Cancer Sup.                        7:1-6,                                                                         1992                                                              Di-/multi-meric                                                                             Pack & Pluckthun, Biochem. 31:1579-84, 1992; H. V. Raff,                       3rd                                                                            IBC Conference on Antibody Engineering, May 14, 1992;                          M. Whitlow, 3rd IBC Conference on Antibody Engineering,                        May 14, 1992; Carter et al., Bio/Immunol. 149:120-6, 1992         Organic molecule mimetics                                                                   Satagovi et al., Science 253:792-5, 1991; Wolf, 3rd IBC           (peptiomimetic)                                                                             Conference on Antibody Engineering, May 14, 1992                  Immunoadhesions                                                                             Marstets et al., J. Biol. Chem. 267:5747-50, 1992; Chatnow,                    et                                                                             al., Int. J. Cancer (Suppl.) 7:69-72, 1992                        Anti-idiotypic antibody                                                                     Escobar et al., Viral Immunology 5:71-79, 1992                    __________________________________________________________________________

In another embodiment of the present invention, the anti-receptor or growth blocking agents' affinity is increased using any one of several means. Retaining high affinity of an antigen-combining site for its target structure is important for a receptor antagonist since its effectiveness is determined by its binding affinity (in combination with half-life). Numerous techniques have been developed that allow one to increase affinity 2-3 fold (and sometimes up to 5-fold) over native antibody including by way of example, cloning antibodies onto an IgM constant region along with joining segments for production of pentavalent antibodies capable of binding multiple binding sites on multiple molecules. (See Table 2.)

In some circumstances, modification of effector functions, either enhancing or decreasing complement-activating ability, or the ability to interact with effector cells would be suitable. Such circumstances include, by way of example, if the antibody was used to remove TcII from incubation. Effector functions of a whole antibody used as a receptor antagonist or growth blocking agent may degrade the selectivity of the receptor antagonist and give more potential for toxicity. Modification of effector function may be determined by any one of several techniques including, by way of example, assays for Fcr mediated binding described in Harel et al., Cancer Res. 50:6311-5315, 1990; Woodhouse, C. S. and A. C. Morgan, Jr., Cancer Res. 49:2766-2772, 1989.

In another embodiment of the present invention, monovalent fragments are engineered into bi- or multi-valent constructs to improve binding affinity. Several post-translational techniques which allow for non-covalent association of monomeric antibody derivatives into multimerit forms can be used to enhance affinity. (See Table 2.) Multi-meric or di-meric forms of antibody fragments may provide advantages from the standpoint of affinity or effector function. Di- or multi-merit molecules may be also more efficient in modulating receptors from surfaces. (See Table 2.)

As discussed in greater detail below, small molecule receptor antagonists are believed to be more useful for certain medical applications due to their low cost, their utility in oral administration and ease of manufacturing. In addition to peptide structures derived from antibodies (molecular recognition units or "MRU"), molecular modeling techniques can be used to create organic molecule mimetics from antibodies using peptide mimetic intermediaries. (see Table 2).

Isolation and cloning of the vitamin B₁₂ /TcII receptor allows the creation of a soluble receptor as a competitor. However, such receptor forms may have a short serum half-life, and poor bio-availability. One way to increase the half-life and bio-availability of these cloned receptors is to attach them by recombinant techniques to immunoglobulin-constant regions. This provides for the longer serum half-life and potential effector functions that may be useful in activity of the receptor antagonist. Such combinations of receptor and immunoglobulin heavy and light chain constant region genes is termed an immunoadhesion.

Using the information present in the combining site of a functional antibody to the B₁₂ /TcII receptor, a second antibody recognizing the combining site of the first can be generated (termed an anti-idiotypic antibody). Such an antibody is the mirror image of the first and thereby an analogue to the receptor itself. Thus, it can be utilized in a manner similar to that of immunoadhesion.

An important step in generating the antibody derivatives discussed above is the isolation of the genes encoding the complementary determining regions (CDR) of an antibody to the B₁₂ /TcII receptor or binding sites. This can be accomplished by any one of a number of techniques. For example, a suitable technique involves immunization of mice, hybridoma formation, and selection to isolate a murine antibody of appropriate specificity. Once murine antibodies are produced, its CDR can be isolated and employed in one of the antibody derivatives identified in Table 2. To elicit such an antibody, the immunogen strategy outlined in Example 1 may be utilized. A similar immunogen approach can be employed in an in vitro immunization scheme where antibodies specific for the B₁₂ /TcII receptor can be elicited and then immortalized through EBV infection, electrofusion or hybrid-hybridoma formation. Alternatively, the genes can be isolated through PCR amplification and then cloned into one of the antibody derivatives previously mentioned.

A human antibody can be produced directly from a specific antibody-producing B-cell from a patient having B-cells sensitized to the vitamin B₁₂ /transcobalamin II receptor or binding sites. In such a case, the human-antibody producing B-cell is identified and immortalized either through a cellular technique or through a gene amplification technique. A source for such a B-cell are patients with pernicious anemia, a congenital abnormality associated with low B₁₂ levels.

In addition, human antibodies may be generated using mice that are transgenic for human immunoglobulin genes. This is accomplished genetically by inserting human IgG genes into the germ line of mice (N. Lonberg, First Annual Meeting on Commercializing human Monoclonal Antibodies, December 17-18, 1992). Alternatively, severe combined immunodeficient (SCID) mice have been transplanted with human leukocytes which will proliferate in the mouse and be available for immunization. (Duchosal et at., Nature 355:258-262, 1992). In this case, the antibody specific for the B₁₂ /TcII receptor or binding sites can be isolated after immunization of the human leukocytes, with an immunogen which enhances the frequency of elicitation of specific antibodies (as described in Example 1 below). Alternatively, antibodies of the appropriate specificity may be generated from combinatorial libraries of germ line IgG genes. In such a process, libraries of Fab fragments, for example, are screened for binding to antigens of the appropriate specificity (essentially equivalent to an un-immunized B-cell repertoire). The same libraries can be created from an immunized repertoire, thus increasing the opportunity for identifying an appropriate antibody. Moreover, the probability of identifying an antibody of appropriate specificity and/or affinity using this technique would be enhanced if prior immunization is carried out following the techniques disclosed in Example 1 below.

Vitamin B₁₂ should be used to overcome any antiproliferative effect of the antibodies on the B-cells from which they originated. Briefly, the antiproliferative effect is a result of the fact that all eukaryotic sources of TcII have considerable amino acid homology due to the common functions of vitamin B₁₂ and receptor binding. However, different species of TcII can be discriminated immunologically. Although polyclonal antibodies in rabbits generally are cross-reactive and are capable of binding both human and mouse TcII, mouse monoclonal antibodies generated to human TcII are not capable of binding both. This indicates that the hybridomas which are cross-reactive are not elicited or not able to expand after elicitation.

This potential problem can be overcome by administering high doses of vitamin B₁₂ which, through passive diffusion, can enter cells without TcII. Any suitable form of vitamin B₁₂ known in the art may be used for supplementation. In a preferred embodiment, the B-cells are cultured in, or the animal vehicle is administered, vitamin B₁₂ preferably in the form of hydroxycobalamin which can bind to serum protein non-specifically.

In another embodiment of the present invention, growth blocking or anti-receptor agents include small organic compounds or peptides. Despite the potential utility of antibodies and antibody derivatives as receptor antagonists, there may be pharmaceutical applications for which they are not appropriate due to their cost, potential for immunogenicity, or need for specialized forms of delivery such as orthotopic or oral administration. For these purposes, small organic compounds or peptides may also be developed. Such peptides and compounds may be developed through: (1) screening of bacterial peptide expression libraries, antibody paratope analogs or antibody Fab expression libraries to identify peptide or antibody variable region inhibitors (Gene 73:305, 1988; Proc. Nat. Acad. Sci. USA 87:6378, 1990; BioChromatography 5:22, 1990; Protein Engineering 3:641, 1989); (2) rational drug design programs using antibodies as a "pharmacophore" to create organic molecule analogs (Biotechnology, Jan. 19, 1991), or traditional rational drug design programs using crystallized vitamin receptor to identify peptide or organic inhibitors (Biochem. J. 268:249, 1990; Science 248:1544, 1990); and (3) screening a library of organic molecules, as present in fermentation broths of microorganisms, for inhibition of vitamin B₁₂ uptake, identifying the biochemical nature of inhibitory compound(s), and chemically synthesizing analogs to explore structure-function relationship and to identify potent inhibitor(s).

Small organic compounds and peptide receptor antagonists for the B₁₂ /TcII receptor or binding sites may be identified through the use of an appropriate assay. In one embodiment, this assay entails tracking the uptake of radiolabeled vitamin B₁₂, complexed with its carrier protein, transcobalamin II. (See Examples 1 and 2 below.) Other assays can also prove useful, including specific binding assays using antibodies which act as competitive antagonists. Through these means a repertoire of protein and non-protein molecules suitable for human use can be generated, and may be used to define optimal regimens to manipulate B₁₂ uptake and bioavailability for different pharmaceutical applications that require an alteration in cellular proliferation.

In one aspect of the present invention, the growth blocking agent is directed to the TcII binding site. (FIG. 4, type 1). Growth blocking agents impede B₁₂ uptake by binding the TcII binding site decreasing or eliminating binding between B₁₂ and TcII. This will affect B₁₂ uptake, since B₁₂ can not enter the cell in effective amounts without binding to TcII. Suitable growth blocking agents are selected using the techniques as described above, and in Examples 8-12. Such antibodies include, by way of example, 2-2, 3-11, and 4-7 (see FIGS. 5, 6, and 7).

In another aspect of the present invention, the growth blocking agent is directed to the holo-TcII binding site. The growth blocking agent bound to this site will affect B₁₂ uptake by preventing the complex from binding to the cell surface receptor. Suitable growth blocking agents are selected as described in detail above and in Examples 8-12. Such antibodies include, by way of example, 2-2, 3-11, and 4-7.

In another aspect of the present invention, the growth blocking agent is directed to the apo-TcII binding site. The growth blocking agent bound to this site will affect B₁₂ uptake by preventing the TcII/B₁₂ complex from binding the cell surface and/or preventing B₁₂ from binding TcII. Suitable growth blocking agents are selected as described in detail above and in Examples 8-12. Such antibodies include, by way of example, 1-18, 5-19, and 7-4 (FIG. 5).

In another aspect of the present invention, the growth blocking agent is directed to any binding sites on TcII or the TcII/vitamin B₁₂ complex which growth blocking agents are capable of binding. The growth blocking agent for this embodiment is capable of redirecting TcII or the TcII/vitamin B₁₂ complex to the reticulo-endothelial organs, such as the liver and spleen, thus affecting B₁₂ uptake. Sequestration of TcII/B₁₂ complex into the liver serves two roles: first, the removal of available vitamin B₁₂ from peripheral tissues, circulating cells and neoplastic disease found therein and second, the provision of vitamin B₁₂ for hepatic function after lysosomal release following endocytosis.

In the case of antibodies, their Fc regions are optimal for interactions with reticulo-endothelial elements. This may be either a property of a given antibody or one achieved by re-engineering. This may include selection of IgM, IgG1, or IgG3 isotypes for a re-engineered antibody or chemical modification to enhance RES removal. For example, in the latter case, conjugation of ligands for the asialoglycoprotein receptor to antibody. Such growth blocking agents are capable of removing 90% of injected material into the liver.

In a particularly preferred method of isolating growth blocking agents, recombinant human TcII, produced by any one of several suitable means including, by way of example, that described in Example 8, is utilized to elicit antibodies using any one of several techniques. Hybridomas are then screened to identify those which recognize recombinant human TcII using any one of several suitable techniques, including by way of example, enzyme linked immunoassay (ELISA). Antibodies which recognize TcII (growth blocking agents) are then tested for the presence of one of the above-described binding sites, using any one of several techniques including, by way of example, radioimmunoassay (RIA). Growth blocking agents may be evaluated for specificity for either holo- or apo- TcII using any one of several techniques, including immunoprecipitation techniques as described in Example 11. Growth blocking agents may be tested for their ability to inhibit uptake of B₁₂ in a biological preparation using any one of several suitable means including, by way of example, a cellular uptake assay as described in Example 10. Suitable selected growth blocking agents may then be purified using any one of suitable techniques, including ELISA sandwich assays and those described in Example 12-14.

Preferably, suitable growth blocking agents have an affinity in the range of about 10⁻⁷ to 10⁻¹⁰ and, even more preferably, greater than 10⁻⁹.

In another aspect of the present invention, the anti-receptor agents are directed to the cell surface receptor, binding to the receptor itself and preventing contact with the carrier protein. Because growth blocking agents described above recognize the CDR, they have an inherent advantage over the receptor-binding anti-receptor agents. The vitamin B₁₂ receptor is expressed at extremely low levels on the cell surface. As a result of this, monoclonal antibodies to the receptor have not been derived to our knowledge, nor has the receptor been purified, sequenced or cloned.

In yet another aspect of the present invention, the anti-receptor or growth blocking agents are used to treat a biological preparation ex vivo or a warm blooded animal. In one treatment aspect of the present invention, the manner in which the antibody-based products of the present invention are used is dependent on the mechanism of action of the anti-receptor or growth blocking agents and their serum half-life. In one embodiment, an anti-receptor or growth blocking antibody acts as an antagonist of the binding of the complex of vitamin B₁₂ /transcobalamin II in a typical mass action fashion. The goal for patient administration is to achieve and maintain serum concentrations of the antibody at a level sufficient to block ≧50%, and more preferably ≧90% or all of the uptake of vitamin B₁₂ into target cells for a prescribed period of time, typically 1 to 7 days. The duration of the blockade is determined by the target cell and the biologic response to be elicited (e.g., cell death or cessation of cell division). One can determine experimentally the degree of inhibition of vitamin B₁₂ uptake by a number of means. If the target cell is one that is easily accessible (e.g., lymphocytes or bone marrow), then samples from patients can be assessed for residual vitamin B₁₂ uptake at various periods following antibody administration.

Alternatively, patient samples can be assessed for binding with FITC conjugated anti-receptor antibody using flow cytometry. If it is difficult to acquire patient samples (as in the treatment of solid tumors), an indirect assessment of receptor blockade may be performed by measuring serum levels of antibody using specific immunoassays (e.g., the use of individually specific anti-idiotypic antiglobulin to measure circulating levels of vitamin B₁₂ receptor antibody or other assays as disclosed below) and referring to amounts of antibody required to maintain receptor blockade in vitro.

The amount of anti-receptor or growth blocking antibody and timing of administration may also be determined using in vitro testing followed by in vivo studies. Primarily, the method used includes measuring serum concentrations, as illustrated in FIG. 2. For example, antibody administered in a dose range of 1 to 500 mg is quantitated in serum by solid phase, competition ELISA using biotinylated anti-receptor antibody binding to a solid-phase receptor source (e.g., glycoprotein isolate from detergent extract of K562 leukemic cells). Unlabeled antibody is used as a competitor to develop a standard curve. As shown in FIG. 2, the serum half-life of a typical IgG antibody is 24 hours, requiring dosing approximately every 36 to 48 hours to maintain serum concentrations above that required for maximal blockade (shown by tri-partite line). The longer the inherent serum half-life of the anti-receptor antibody, the fewer administrations required. Thus, an IgM antibody with a half-life of several days may be more advantageous under certain circumstances. If, for example, plasma concentration of TcII is 30 picograms/mL or 96 micrograms for the entire body, there is about 10% holo-TcII. The steady state synthesis allows for replacement of 80 μg of TcII/B₁₂ complex every 24 hours. Assuming a 10 fold antibody to the binding site and an antibody 1/2 life of 48 hours, then the warm-blooded animal would only require 2 mg/48 hours.

Antibodies capable of modulating or "capping" vitamin B₁₂ receptors may be used in a manner similar to competitive antagonists. However, knowledge of the parameters of receptor modulation is necessary to optimize therapy. Modulation, capping, patching, clustering, or immobilization can be the result of interactions of antibodies with cell surface antigens or receptors. The terms describe a range of responses from complete clearance of antigen from the surface to an inhibition of antigen mobility within the membrane. Whatever type of interaction occurs, antibody binding can result in a loss of function or triggering of a biological response, depending on the nature of the antigen. There have been a variety of antigens and receptors demonstrated to undergo modulation when bound by antibody, but there appears to be little relationship between antigen number and the ability to be modulated (Acta Haemotol. 73:196, 1985). Since bivalency (or multi-valency) is required to cross-link antigen and cause modulation, the ability to do so is governed by antigen density and distribution, as well as the distance spanned by antibody (e.g., an IgM can span a greater distance than IgG). In addition, accessory antigens, antibodies or cells can also enhance modulation. For instance, modulation of receptors is enhanced by the presence of complement, by HIV gp120 protein for CD-4 on T-cells, and by monocytes for CD-5 modulation on T-cells (J. Immunol. 133:2270, 1984; Science 245:1380, 1989; J. Immunol. 144:239, 1990).

In one treatment aspect of the present invention, anti-receptor or growth blocking agents are employed to create a transient state of TcII deficiency. This transient deficiency results in an inhibition of uptake of TcII/vitamin B₁₂ onto the cellular receptor, cellular depletion of vitamin B₁₂ and, ultimately, in death to tumor cells. Depending on the type of neoplastic disorder and the tumor burden, the duration of the transient deficiency may be optimally varied from one to six weeks (see Example 4). TcII is rapidly synthesized. Thus, cessation of antibody treatment will result in reinstitution of normal TcII/vitamin B₁₂ levels. Alternatively, patients may be treated with vitamin B₁₂ or folate to reverse the effects of the antibody treatment.

Essential for modulation is the epitope on the target antigen, recognized by antibody. J. Immunol. 137:2286, 1986. In the case of cell surface IgD immunoglobulin on B-cells, antibodies modulate according to the portion of the cell surface IgD molecule bound. J. Immunol. 139:2873, 1987. Once modulated, antigen or receptor can have several fates: immobilization or clustering on the cell surface, internalization and degradation or shedding. The degree of modulation may vary significantly even with the same antibody, antigen, and target cell population. Acta Haematol. 76:119, 1986. Whichever fate, biological responses may be suppressed or triggered by modulation and not be reestablished for periods of 24 to 72 hours, coincident with antigen or receptor re-expression.

Selectivity may be achieved in modulation also. Most types of cells can be modulated by antibodies as described for fibroblasts (J. Cell Sci. 98:191, 1991), adipocytes (Int. J. Immunopharmacol. 6:193, 1984), pancreatic islet cells (Diabetologia 24:117, 1983), sperm (Exp. Cell Res. 144:275, 1983), glomerular epithelium (J. Immunol. 135:2409, 1985) and tumor cells (Int. J. Cancer 448:1095, 1989). However, modulation is most readily achieved on lymphoid cells. Depending on the tissue location, such lymphocytes may be more or less susceptible to modulation. For instance, antibody to OKT-3 like antigens on guinea pig T-cells were susceptible to modulation when present in all lymphoid tissues except thymus. J. Immunol. 138:2500, 1987. CD-5 antigen or human T-cells can be modulated on peripheral cells without modulation of T-cells in lymph nodes by controlling the dose of antibody. The reverse can also be achieved by injecting a modulating dose of T101 (anti-CD-5) for peripheral cells, and following with a subsequent second infusion of T101 which is delivered selectively to lymph node T-cells (J. Immunol. 133:1641, 1984; N. Eng. J. Med. 315:673, 1986). Modulation is not restricted to just antibodies; small compounds and peptides can also cause redistribution of a receptor (J. Biol. Chem. 167:3530, 1992).

Common to many non-neoplastic disease processes is a stage in which the disease process itself, or its symptoms, can be halted or ameliorated by the use of an anti-proliferative agent such as vitamin B₁₂ receptor antagonists. These commonly recognized stages include a sensitization or elicitation phase in which immune cells responsible for the disease become turned on by antigen specific or non-specific means, followed by a proliferative phase in which the immune cells expand in number, and finally a symptomatic phase in which the expanded immune cells create tissue damage directly or indirectly. Because of this, anti-proliferative chemotherapeutic drugs are commonly utilized in the treatment of many diseases other than cancer, but are limited in use to life threatening situations due to their associated toxicity. Anti-proliferative agents, such as the ones of the present invention (with little of the direct toxicity of chemotherapeutic drugs), may be used more widely. More specifically, the anti-receptor agents of the present invention are not destructive to plasma membrane processes (e.g., ion transport). In addition, the anti-proliferative activity is reversible by administration of vitamin B₁₂. Furthermore, the agents of this invention may not be mutagenic, teratogenic, or carcinogenic since they act at the level of the plasma membrane, and not at the level of the nucleus, and DNA by intercalation or cross-linking (as many chemotherapeutic drugs act).

In another treatment aspect of the invention, growth blocking agents are administered following courses of treatment with chemotherapeutic drugs, regardless of whether or not they were administered with or before the treatment. Growth blocking agents can be administered to patients for prolonged periods of time (i.e., months) in the adjuvant setting, in order to check proliferation of any neoplastic cells that have not been killed by the prior treatments.

An understanding of the pharmaceutical applications for B₁₂ /TcII receptor antagonists requires a knowledge of the cell types targeted by such therapy. To this end, various pharmaceutical applications are disclosed in Table 3 below.

                  TABLE 3                                                          ______________________________________                                         Target Cells for Vitamin B.sub.12 Receptor Antagonists                                   Other Proliferation                                                                          Potential Pharmaceutical                               Target Cell                                                                              Associated Markers                                                                           Applications                                           ______________________________________                                         Activated T-Cell                                                                         IL-2 receptor Graft versus Host Disease                                        Transferrin Receptor                                                                         Organ Transplants                                                Insulin Receptor                                                                             Auto-Immune Diseases                                             Class II Histocompati-                                                                       Asthma                                                           bility Antigens                                                                              Crohn's Disease                                        Tumor Cells                                                                              Tumor Assoc. Ags.                                                                            Tumor Therapy                                                    Ki67          (alone and in combination                                        Transferrin Receptor                                                                         with chemotherapeutic drugs)                           Bone Marrow                                                                              CD-34         Allogeneic Bone Marrow                                 Stem Cells                                                                               Transferrin Receptor                                                                         Transplants                                                      Class II Histocompati-                                                                       Reduction in Toxicity of                                         bility Antigens                                                                              Chemotherapy                                                     IL-1, IL-3 Receptors                                                 Proliferating                                                                            Thy 1.1       Inhibition of Adhesions,                               Fibroblasts                                                                              Transferrin Receptor                                                                         Scarring                                                         Insulin & Insulin-like                                                                       Scleroderma                                                      Growth-Factor                                                                  Receptors                                                                      Fibroblast Growth-                                                             Factor Receptor                                                      Proliferating                                                                            EGF Receptor  Psorasis                                               Epithelium or                                                                            Proto-Oncogenes                                                      Epidermal                                                                      (Keratinocytes)                                                                ______________________________________                                    

Proliferating and activated T-cells can cause a wide variety of diseases ranging from the chronic intimation of Crohn's disease to more acute organ graft rejection. In all of these diseases, the T-cell may serve a central pathogenic role or a more accessory role. Anti-proliferative chemotherapeutic drugs serve to reduce symptomotology and in some cases lead to long-term remission. Similarly, proliferating fibroblasts and epithelial cells may give rise to diseases characterized by cell overgrowth. Vitamin B₁₂ receptor agents may be used to replace or used in combination with existing chemotherapeutic regimens in these diseases. An important aspect of the use of anti-proliferative vitamin B₁₂ receptor agents in these diseases is not to apply it so aggressively or with improper timing such that normal healing (adhesions, scarring) or cell renewal (psorasis) processes are also inhibited. As such, low doses of anti-receptor agents may be used during healing and higher doses once healing is completed. Alternatively, anti-receptor agents may not be administered at all until after healing is completed.

As previously mentioned, B₁₂ /TcII receptor antagonists or growth blocking agents can be used to deprive neoplastic cells of vitamin B₁₂. It has already been shown that sufficient deprivation leads to the death of rapidly proliferating lymphoid neoplasm such as leukemia and lymphoran. Moreover, short term treatment to reduce cellular availability of this nutrient, combined with existing chemotherapeutic agents, markedly improves therapeutic efficacy.

For solid tumors, B₁₂ depletion may induce cytostasis and differentiation as well as apoptosis or cell death. Thus, B₁₂ /TcII receptor antagonists or growth blocking agents may be used to induce differentiation in hormonally responsive solid tumors. An increase in the number of cells expressing a differentiated phenotype should translate into an increase in expression of hormone receptors. The hormone receptor status of tumors, such as breast and prostrate cancer, are directly correlated with their response to hormonal therapy. Accordingly, B₁₂ /TcII receptor antagonists or growth blocking agents can be used to increase the number of receptor positive tumor cells or increase receptor density in order to enhance efficacy of subsequent hormonal therapy.

Vitamin B₁₂ receptor antagonists or growth blocking agents may affect both replicating neoplastic and normal cells. However, bone marrow progenitors demonstrate differential sensitivity or response. Thus, B₁₂ receptor antagonists or growth blocking agents can be used to modulate sensitivity of bone marrow progenitors so as to enhance their resistance to the toxic effects of chemotherapeutic agents. Such chemotherapeutic drugs act primarily on replicating cells, with non-replicating cells being much less sensitive. Antibodies are well suited for this application since delivery is more readily achieved to highly accessible marrow versus normal organs and solid tumors. In addition, a B₁₂ /TcII anti-receptor or growth blocking antibody, possessing the ability to modulate a receptor or binding sites, could differentially effect lymphoid versus epithelial tissues. Decreasing the sensitivity of progenitors to toxic drugs would increase the bone marrow reserves and enhance subsequent response to colony stimulating factors, and enable higher doses of chemotherapy or reduce the interval to reconstitution. It should also be recognized that such positive effects on bone marrow progenitors, as a natural consequence of B₁₂ receptor therapy for cancer, is an additional mechanism by which the therapeutic index of chemotherapeutic drugs other than 5-FU and methotrexate can be improved.

In a variety of autoimmune diseases, graft versus host disease, ectopic allergy, and organ transplantation, an initial "induction" phase, in which the patient becomes sensitized to self or allo-antigens, is followed by a "proliferative" phase in which forbidden or unregulated clones of B- or T-cells are expanded. It has long been known that treatment with anti-proliferative, chemotherapeutic drugs following induction can inhibit expansion of forbidden clones, inhibit progression of disease, and restore a stable state of tolerance. An antibody, OKT-3, that controls the proliferation of allo-antigen-sensitized T-cells, has been approved for management of acute allograft rejection. Anti-receptor antibodies of the present invention can be substituted for extremely toxic chemotherapeutic drugs or highly immunogenic antibodies such as OKT-3 and achieve a similar state of tolerance without these associated drawbacks.

Inflammation is an application for which antibodies are already being utilized in clinical trials. The primary emphasis has been on inhibiting the early manifestations of inflammation by inhibiting recruitment or binding of inflammatory cells to vascular endothelium of injured tissue. It also well recognized that proliferation of cells at the site of inflammation contributes to the pathology and tissue destruction of both acute as well as chronic inflammation. To this end, anti-proliferative, chemotherapeutic drugs have been widely used to inhibit sequelae of inflammation.

Methotrexate is one such drug commonly used to treat symptoms associated with rheumatoid arthritis. The drug acts to reduce both localized (e.g., synovium) and generalized inflammation associated with disease progression. Methotrexate acts synergistically with vitamin B₁₂ depletion in therapy of leukemia. B₁₂ antagonists can therefore be combined with methotrexate to enhance efficacy in rheumatoid arthritis. Other methotrexate applications include treating destructive inflammation associated with chronic heart disease and colitis.

Surgery, radiation or chemotherapy to the abdomen is often complicated by the development of tissue adhesions. These represent a considerable clinical problem because they lead to bowel blockage and require surgical intervention. Peritoneal adhesions arise as a result of proliferation of the cells of the peritoneal membrane lining the abdomen. A non-toxic means of interfering with such proliferation could lead to restoration of these normal cells to homeostatic control mechanisms and thereby inhibition of adhesion formation. A similar process of benign proliferation and subsequent scarring is a complication of retinal surgery. Direct instillation of a small molecule analog of an antibody receptor antagonist could prevent such disabling complications.

The growth blocking or anti-receptor agents are administered in a therapeutically effective dose which may be determined by in vitro experiments followed by in vivo studies. A therapeutically effective dose of growth blocking or anti-receptor agent and the timing of administration are determined by any means known in the art, including by measuring serum concentrations. For example, antibody administered in a dose range of 1 to 500 mg is quantitated in serum by solid phase, competition ELISA using biotinylated growth blocking agent binding to a solid-phase binding site source (e.g., purified, serum, TcII or recombinant TcII. Unlabeled antibody is used as a competitor to develop a standard curve while growth blocking agents in serum aliquots is quantitated. As shown in FIG. 2, the serum half-life of a typical IgG antibody is 24 hours, requiring dosing approximately every 36 to 48 hours to maintain serum concentrations above that required for maximal blockade (shown by tri-partite line). The longer the inherent serum half-life of the growth blocking or anti-receptor agent, the fewer administrations required. Thus, an IgM antibody with a half-life of several days may be more advantageous under certain circumstances.

The term "treatment" as used within the context of the present invention, refers to reducing or alleviating symptoms in a subject, preventing symptoms from worsening or progressing, inhibition or elimination of the causative agent, or prevention of the infection or disorder in a subject who is free therefrom. Thus, for example, treatment of infection includes destruction of the infecting agent, inhibition of or interference with its growth or maturation, neutralization of its pathological effects and the like. A disorder is "treated" by partially or wholly remedying the deficiency which causes the deficiency or which makes it more severe. An unbalanced state disorder is "treated" by partially or wholly remedying the imbalance which causes the disorder or which makes it more severe.

Pharmaceutical compositions containing the growth blocking or anti-receptor agents in an admixture with a pharmaceutical carrier or diluent can be prepared according to conventional pharmaceutical compounding techniques. The carrier may take a wide variety of forms depending on the form of preparation desired for administration, e.g., intravenous, oral topical, aerosol, suppository, parenteral or spinal injection.

The following examples are designed to illustrate the production and use of certain vitamin B₁₂ /TcII receptor antagonists and modulators and growth blocking agents. The type of receptor antagonist and modulator used in the examples is a human or chimeric antibody applied to the treatment of AIDS Related Lymphoma (ARL), a particularly aggressive form of cancer arising in AIDS patients, as well as other medical applications. Small molecule and peptide analogs may also be used for treatment of cancer, but are more optimally used in other pharmaceutical applications. The following examples are offered by way of illustration and not by way of limitation.

EXAMPLES Example 1 Identification and Characterization of Functional Monoclonal Antibodies to the Vitamin B₁₂ Receptor

Hybridomas are generated by PEG mediated fusion of murine splenocytes from mice, immunized as shown in FIG. 1, and HGPRT- myeloma cells like NS-1. For immunogens, transcobalamin II, present in Cohn-purified serum protein, is covalently immobilized (CnBr Sepharose) and used to adsorb small quantities of solubilized receptor. The complex is then used to immunize mice. Four to six weeks after fusion, hybridoma supernatants are screened in a functional assay for inhibition of vitamin B₁₂ uptake in K562 leukemic cells cultured in chemically defined medium using a modified radio labeled assay with 57 Co-vitamin B₁₂ complexed with transcobalamin II from Cohn fractions. The results of the primary screen in microtiter plates are illustrated in Table 4 below and expressed as the fraction of the uninhibited control (well A1). Well H12 serves as the positive control (maximum inhibition) and utilizes serum as a source of unlabeled vitamin B₁₂ complexed to transcobalamin II as competitor.

                                      TABLE 4                                      __________________________________________________________________________     Primary Screen of Hybridomas                                                   1    2   3  4  5  6  7  8  9  10 11 12                                         __________________________________________________________________________     A 1.000                                                                             .986                                                                               .995                                                                              .973                                                                              .322                                                                              .898                                                                              .994                                                                              .993                                                                              .982                                                                              .988                                                                              .987                                                                              1.000                                      B .788                                                                              .922                                                                               .888                                                                              .965                                                                              .986                                                                              .923                                                                              .898                                                                              .993                                                                              .942                                                                              .986                                                                              .897                                                                              .954                                       C .972                                                                              >1.000                                                                             .984                                                                              .832                                                                              .964                                                                              .777                                                                              .885                                                                              .924                                                                              .987                                                                              .845                                                                              .892                                                                              1.000                                      D .983                                                                              .111                                                                               .986                                                                              .799                                                                              .912                                                                              .943                                                                              1.000                                                                             .956                                                                              .964                                                                              .955                                                                              .913                                                                              .987                                       E .788                                                                              .922                                                                               .888                                                                              .965                                                                              .986                                                                              .923                                                                              .898                                                                              .993                                                                              .942                                                                              .986                                                                              .897                                                                              .954                                       F 1.000                                                                             .986                                                                               .995                                                                              .973                                                                              .988                                                                              .898                                                                              .994                                                                              .993                                                                              .982                                                                              .198                                                                              .987                                                                              1.000                                      G .983                                                                              .986                                                                               .986                                                                              .799                                                                              .912                                                                              .943                                                                              1.000                                                                             .956                                                                              .964                                                                              .955                                                                              .913                                                                              .987                                       H .972                                                                              1.000                                                                              .984                                                                              .832                                                                              .964                                                                              .777                                                                              .885                                                                              .924                                                                              .987                                                                              .845                                                                              .892                                                                              .089                                       __________________________________________________________________________

The hybridomas identified in this primary screen (AS, C2, D2, and F10) are cloned by limiting dilution with thymic feeder cells. Four to six weeks later, clones (identified by sequential numbering) from the primary wells are rescreened in the functional assay to identify those clones retaining the characteristic activity of the parents. In addition other assays are performed to characterize the specificity of the clones by inhibition of vitamin B₁₂ uptake on carcinoma versus leukemia cells or normal, mitogen stimulated lymphocytes. The results of the assessment of specificity are shown in Table 5 below.

                  TABLE 5                                                          ______________________________________                                         Assessment of Specificity                                                      Clone      Target Cells                                                        Lymphocytes                                                                               Carcinoma    Leukemia Normal                                        ______________________________________                                         A5/8       .386         .333     .287                                          A5/12      .342         .384     .317                                          C2/2       .989         >1.000   >1.000                                        C2/5       .923         >1.000   >1.000                                        D2/20      .656         .089     .154                                          D2/7       .891         .174     .245                                          F10/4      .198         .123     .423                                          F10/8      .234         .312     .666                                          ______________________________________                                    

Based upon these results the antibody D2/20 is selected for further evaluation in treatment of lymphoma. The antibody is able to strongly inhibit vitamin B₁₂ uptake at levels of antibody as low as 10 nanograms/ml (not shown). In addition, the antibody appears to inhibit uptake of vitamin B₁₂ in lymphoid cells but not those of epithelial origin, a characteristic which is potentially useful in decreasing toxicity to replicating crypt cells in colonic epithelium. In other assessments, the antibody did not inhibit uptake of vitamin B₁₂ in mitogen stimulated murine splenocytes, indicating its specificity for the human receptor.

Example 2 In Vitro Assessment of Cell Killing Potential of Vitamin B₁₂ Anti-Receptor Antibody Alone and In Combination with Chemotherapeutic Drugs

Antibody D2/20 at a range of concentrations is incubated with Raji Burkitt lymphoma cells in microtiter plates for three days with and without chemotherapeutic drugs. Cell viability is measured by reduction of tetrazolium dye. Only viable cells metabolize the dye to an insoluble, colored product which is subsequently solubilized and read in a spectrophotometer. The results of the assay are shown in Table 6 below.

                  TABLE 6                                                          ______________________________________                                         Antibody (nanograms/ml)                                                        100    10       1      0                                                       ______________________________________                                         .268   .435     .723   .987   0    Methotrexate                                .055   .077     212    .993   0.1  (micrograms/ml)                             .048   .052     .089   .798   1                                                .047   .048     054    .563   10                                               ______________________________________                                          100% lysis control = .047                                                

Based on these results, the antibody to the vitamin B₁₂ receptor is able to elicit cell death of the lymphoma cells, presumably by starving them of vitamin B₁₂. In addition, when combined with methotrexate, the combination appears to be synergistic since it was considerably more active than either of the two agents alone. The results are consistent with those obtained with other methods of vitamin B₁₂ depletion.

Example 3 In Vivo Assessment of Vitamin B₁₂ Anti-Receptor Antibody in Combination with Chemotherapeutic Drug

Nu/nu mice are injected subcutaneously with 1 million Raji Burkitt lymphoma cells. After two weeks, barely palpable nodules are present at the injection site. Measurements are made in three dimensions with a planarimeter and equally sized tumors assigned to experimental groups of 10 mice. Mice are injected intravenously with the drug, methotrexate (3 dose levels-50, 10, and 5 milligrams/M²) and antibody D2/20 at 100 micrograms/mouse. Therapy is administered once weekly. Controls of antibody and drug alone, as well as vehicle controls, are included. Mice are monitored visually for toxicity, death, and tumor size weekly for 8 weeks, at which time the experiment is terminated, the mice sacrificed, and the tumors removed and weighed. The average of serial tumor measurements converted to weight (grams) is shown in Table 7 below.

                  TABLE 7                                                          ______________________________________                                                  Week                                                                  Group    1     2      3   4    5    6     7    8                               ______________________________________                                         Vehicle  .05   .12    .34 .67  1.3  2.9   6.0  --                              Antibody .06   .09    .12 .22  .35  .57   .83  1.02                            (Ab)                                                                           Drug     .04   .10    .25 .41  .73  1.4   2.3  3.4                             (50)                                                                           Drug     .05   .12    .30 .53  .92  2.1   4.8  6.9                             (10)                                                                           Drug     .07   .14    .43 .70  1.2  2.6   4.8  7.2                             (5)                                                                            Ab + Drug                                                                               .05   .07    .11 .09  N.D. N.D   N.D. N.D.                            (50)                                                                           Ab + Drug                                                                               .06   .08    .13 .15  .12  .07   N.D. N.D.                            (10)                                                                           Ab + Drug                                                                               .05   .07    .11 .21  .24  .17   .15  .11                             (5)                                                                            ______________________________________                                          (--) = Not measurable due to tumor necrosis                                    N.D. = Not detectable                                                    

Based upon these results, it can be concluded that vitamin B₁₂ anti-receptor antibody is active in inhibiting tumor growth in this model of human Burkitt lymphoma, and that its combination with methotrexate provides a more effective regimen.

Example 4 Treatment of a Patient with AIDS Related Lymphoma with Vitamin B₁₂ Anti-Receptor Antibody in Combination with Chemotherapy

A patient diagnosed with AIDS Related Lymphoma is admitted to the hospital for treatment. The patient presents with CNS involvement and poor prognosis and is suffering from a fever of unknown origin. The patient has CD-4 counts below 200/μl and has been receiving anti-retroviral therapy, AZT (zidovudine), prior to diagnosis of ARL. The patient is given an aggressive regimen combining chemotherapy with bone marrow support (rGM-CSF) according to the following protocol:

A. Cyclophosphamide, 200 mg/M², IV over 30 minutes daily on days 1 through 5;

B. Vincristine 1.4 mg/M² IV push on day 1, not to exceed 2 mg/dose;

C. High dose methotrexate, 1500 mg/M² day 1, 150 mg/M² administered over 30 minutes with the subsequent 1350 mg/M² administered over the next 231/2 hours, rapid urine flow maintained with the urine pH's supplemented with sodium bicarbonate to maintain the urine pH>7.5;

D. Folinic acid, 30 mg IV or PO administered q6h, beginning 12 hours after the completion of the methotrexate infusion, folinic acid continued until the serum methotrexate level is 0.01 uM;

E. Mitoxanthrone, 10 mg/M2 IV push on days 4 and 5;

F. Decadron, 5 mg/M2 IV push on days 4 and 5;

G. rGM-CSF, 3 μg/kg subcutaneously bid, through day 6, until the absolute granulocyte count is >1,000/ul; and

H. Cytarabine (50 mg) intrathecal on day 1 of course 1; thereafter intrathecal methotrexate (12 mg) on day 1 and intrathecal cytarabine on day 16 for each of 6 other courses of therapy.

The patient is also administered antibiotics and Diflucan prophylactically. AZT is discontinued during chemotherapy. The patient receives seven courses of therapy and is assessed to have experienced a partial response of nodal disease and a complete response of CNS disease. After 7 months the patient returns to the hospital with relapsing disease peripherally, but still negative for CNS involvement.

The patient is treated with the same combination regimen with the following exceptions: rGM-CSF is not included due to concerns for accelerating tumor growth, no intrathecal treatment, and the inclusion of vitamin B₁₂ receptor antibody. In particular, antibody is administered on day 1 of each course of chemotherapy. The antibody component of the regimen consists of a "humanized" chimeric IgM derived from the murine antibody D2/20, administered at a dose of 100 mg in a IV drip over 4 hours. The antibody has been previously determined to have a serum half-life of 72 hours in patients.

The patient is removed from treatment after only 3 courses due to a non-responding neutophil count due to the lack of rGM-CSF. After 4 months however, the patient is assessed to have experienced a complete response of peripheral disease. The patient continues in complete response for 17 months.

Example 5 Identification of Monoclonal Antibodies Capable of Vitamin B₁₂ Receptor Modulation

The hybridomas positive in the assay for inhibition of Vitamin B₁₂ uptake (Example 1 above) are screened in a different assay designed to identify those hybridomas capable of receptor modulation. Hybridoma supernatants are incubated with 1×10⁶ K562 leukemic cells at 4° C. for 60 minutes. Cells are resuspended, washed and an equal aliquot of cells (5×10⁵) removed to a separate tube and incubated at 37° C. for 60 minutes while the other aliquot is retained at 4° C. for the same period. Both aliquots from each hybridoma are analyzed for bound mouse immunoglobulin by staining with fluorescein isothiocyanate-conjugated, anti-mouse immunoglobulin (FITC-αMIg). Unbound, secondary antibody is removed by washing, and stained cells examined using a Coulter Epics C flow cytometer. The mean fluorescent intensity (MFI) of positive cells and the binding profile are compared on the two aliquots .of cells. Of the antibodies identified in Example 1, only the sister clones F10/4 and F10/8 are positive for receptor modulation as shown in FIG. 3. Fluorescence intensity of the sample held at 37° C. is significantly lower than the one held at 4° C., and constitutes preliminary evidence of receptor modulation.

Parameters for receptor modulation or "capping" are further detailed by studies with microtubule and microfilament inhibitors like colchine or vinblastine, to demonstrate the requirement of cytoskeleton in modulation. Studies are also performed with sodium oxide to demonstrate the dependence of capping on cellular energy processes. In addition, the time to complete expression of receptors is determined to be 24 hours, and it is determined that only nanogram/ml levels of antibody are required to maintain cells devoid of receptors which results in complete inhibition of thymidine uptake within 72 hours.

Example 6 Treatment of a Patient with Graft Versus Host Disease (GVHD) with Vitamin B₁₂ Anti-Receptor Antibody

An adult patient with acute leukemia enters the hospital for an induction regimen prior to bone marrow transplantation. The patient receives cytosine arabinoside, 3 g/M², every 12 hours for 6 days, followed by fractionated total body irradiation, 200 cGy, twice daily for 3 days. The patient is administered T-cell depleted, histocompatible marrow following induction, along with cyclosporine and methotrexate for prophylaxis of GVHD. The cyclosporine is administered through a silastic catheter from day 1 through day 180 at a dose level of 1.5 mg/Kg/d for the first 15 days, followed thereafter at a dose level of 3 mg/Kg/d. Methotrexate is administered at a dose of 0.25 mg/Kg/d on days 1, 3, 6, 11, 18, 25, and 31.

The patient demonstrates engraftment and has no evidence of GVHD up to 3 months. At that time, however, the patient is readmitted to the hospital and diagnosed as suffering from Grade III GVHD while still receiving cyclosporine A. The patient is once again administered methotrexate but in combination with Vitamin B₁₂ anti-receptor antibody. The regimen consists of administration of a "humanized" chimeric IgM derived from the murine antibody F10/4 at a dose of 50 mg in an IV drip over 4 hours followed by methotrexate infusion (0.25 mg/Kg/d). The regimen is administered on days 1, 3, 6, and 11 while maintaining cyclosporine administration. After two weeks most manifestations of GVHD have resolved and the patient is maintained on cyclosporine for an additional 60 days. The patient remains free of GVHD for two years at which time he relapses from leukemia and dies.

Example 7 Reduction in Hematologic Toxicity of Chemotherapeutic Drugs with Vitamin B₁₂ Anti-Receptor Antibody

A patient with stage IV colon cancer with both lymph node and liver involvement is admitted to the hospital for treatment. The patient is administered a regimen of leucovorin (200 mg/M²), given as a 10-minute infusion, followed by a dose of 1,000/M² of 5-fluorouracil every two weeks. Therapy is stopped after 2 months due to grade III/IV leukopenia and thrombocytopenia. The patient experiences a partial response of liver and lymph node disease and only minimal neurotoxicity.

The patient is re-treated by prior infusion of an IgM, "humanized" chimera of antibody F10/4, capable of modulating the vitamin B₁₂ receptor. The patient is infused with 2 mg of antibody over 2 hours, a dose found previously to modulate the receptor on bone marrow cells, but which is virtually undetectable by immunoperoxidase in biopsies of solid tumor lesions of patients. After 18 hours the patient is infused with 5-fluorouracil and leucovorin as before. The patient continues receiving treatment every 2 weeks for 4 months and experiences only Grade I thrombocytopenia and moderate neurotoxicity. After this second treatment interval, the patient is assessed to have experienced a complete response of lymph node disease with a virtual complete response of liver disease.

Example 8 Production of Recombinant TcII

Preparation of the TCII cDNA. The full-length cDNA for TCII that was previously isolated from a human endothelial cell cDNA library in λ gt II and subcloned into PGEM 3Z f (-) vector, Platica, O. et al., "The cDNA sequence and the deduced amino acid sequence of human transcobalamin II show homology with rat intrinsic factor and human transcobalamin II," J. Biol. Chem 266:7860, 1991, was amplified in liquid culture and isolated by alkaline lysis and cesium chloride gradient centrifugation, Sambrook J. et al., "Molecular Cloning, A Laboratory Manual" Cold Spring Harbor Laboratory Press, 1989. The plasmid was digested with EcoRI and the cDNA insert was separated by electrophoresis in 0.8% low melting point (LMP) agarose gel, and recovered from the agarose by phenol extraction followed by ethanol precipitation, Sambrook J. et al., "Molecular Cloning, A laboratory Manual, Cold Spring Harbor, N.Y.," Cold Spring Harbor Laboratory Press, 1989.

Insertion of the cDNA into a plasmid vector for baculovirus. The plasmid, PVL 1393, Webb, N. R. et at., "Expression of proteins using recombinant baculoviruses," Technique 2:173, 1990, was amplified in Escherichia coli JM 109 and purified by cesium chloride gradient centrifugation, Sambrook J. et al., "Molecular Cloning, A Laboratory Manual," Cold Spring Harbor Laboratory Press, 1989. To insert the TCII cDNA into this vector, the plasmid was linearized by EcoRI digestion and isolated from LMP agarose following electrophoresis. The full-length TCII cDNA (1866 bp) encompassing a 54-nucleotide (nt) leader peptide, a 37-nt 5' untranslated region, and a 548-nt 3' untranslated region, including the polyadenylation signal, was inserted into this plasmid, and clones containing the cDNA in the correct orientation for the translation of the protein were identified by the predicted size of the fragments following digestion of the insert containing plasmid with restriction enzymes.

Culture of SF9 cells. SF9 cells (ATCC 1711-CRL) were propagated at 27° C. in TNM-FH medium (Sigma Chemical Co, St. Louis, Mo.) and supplemented with 10% heat inactivated fetal bovine serum (FBS) (GIBCO, Grand Island, N.Y.) as described by Summers and Smith. Summers, M. et at., "A manual of methods for baculovirus vectors and insect cell culture procedures," Texas Agricultural Experiment Station Bulletin No. 1555, College Station, Tex., Texas A&M University, 1987.

Isolation of the wildtype baculovirus. SF9 cells were infected with Autographa californica nuclear polyhedrosis virus (AcNPV) at a multiplicity of infection (MOI) of 10. Following incubation at 27° C. for 72 hours, the medium was collected, and the extracellular virus in the medium was collected, and the extracellular virus in the medium was purified by sucrose density gradient centrifugation.

Generation and isolation of recombinant virus. The production and isolation of recombinant virus was performed as described by Summers and Smith, Summers, M. et al., "A manual of methods for baculovirus vectors and insect cell culture procedures," Texas Agricultural Experiment Station Bulletin No. 1555, College Station, Tex., Texas A&M University, 1987, using the calcium phosphate transfection protocol. Graham, FL et al., "A new technique for assay of infectivity of human adenovirus 5 DNA," Virology 52:456, 1973. The recombinant virus in the 96-hour post-transfection medium was purified by plaque assay in LMP agarose plates. Recombinant plaques were identified by visual screening and confirmed by dot-blot hybridization of DNA from infected SF9 cells using the TCII cDNA as the probe. All subsequent assays for the recombinant virus were performed by measuring the binding of ⁵⁷ Co!B₁₂ (Amersham, Arlington Heights, Ill.) to recombinant TCII in the postculture medium of SF9 cells infected with virus recovered from individual plaques.

Purification of recombinant TCII. The culture medium from SF9 cells infected with recombinant virus for 100 to 120 hours was collected, and the cell debris was removed by centrifugation at 3,000 g for 15 minutes. The recombinant TCII was purified by affinity chromatography using the photo-labile B₁₂ -propyl-Sephacryl (Pharmacia LKB) as described previously, Quadros, E. V. et al., "Purification and molecular characterization of human transcobalamin II," J. Biol. Chem 261:15455, 1986, with the following modification; for the batchwise purification of TCII, 2 g CM-Sephadex C-50 (Pharmacia LKB) was added to each liter of culture medium, which had been titrated to pH 5.2 with 1N HCl. The final step of the purification procedure as previously described, Quadros, E. V. et at., "Purification and molecular characterization of human transcobalamin II," J. Biol. Chem 261: 15455, 1986, was omitted, because the protein released from the affinity matrix was devoid of any contaminating proteins as determined by sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE).

Example 9 Production of Antibodies to TcII

Murine monoclonal antibodies were produced by conventional methods from immunized animals using recombinant human TcII produced in Example 8. The hybridomas were cultured and plated. Wells demonstrating hybridoma growth were screened for the presence of antibodies against TcII by the enzyme linked immunoabsorbent assay ("ELISA") as described in Hermanson et al., Immobilized Affinity Ligand Techniques, Academic Press, 1992. Positive wells were identified and then tested for presence of antibodies against apo-TcII (FIG. 4, type 1) by measuring their ability to prevent binding of ⁵⁷ Co labeled vitamin B₁₂ to TcII in a radioimmunoassay (RIA). TcII is coated onto microtiter plates. Radiolabeled B₁₂ and the antibody sample are incubated on the plate for three (3) hours at 37° C. After decanting the mixture and washing the microtiter plate with PBS X3, the radioactivity of the plate is measured. The results are reported as percentage inhibition in FIG. 5.

Example 10 Assay for Cellular Uptake of Holo-TcII used to Isolate Monoclonal Antibodies which Inhibit Cellular Uptake of Vitamin B₁₂.

The ELISA data generated in Example 9 was then used to select hybrids to test for ability to inhibit uptake of the labeled B₁₂ in a biological preparation. 1-18, 2-2, 3-4, 3-11, 3-16, 4-4, 4-7, 5-2, 5-12, 5-4, 5-19, 6-4, 6-13, 7-4, 8-4, and 5-18 were chosen on the basis of their performance as evaluated by the ELISA.

Human erythroleukemia cells K562 (ATCC accession number CCL 243) were used to evaluate vitamin B₁₂ uptake. They were typically cultured for 48 to 72 hours in RPMI 1640 medium containing 10% fetal bovine serum before use. Vitamin B₁₂ labelled with ⁵⁷ Co (Amersham, Arlington Heights, Ill. or Eastman Kodak, Rochester, N.Y.) in a volume of 100 uL was first bound to TcII in a volume of 500 uL by mixing and incubation at room temperature for 30 minutes. The TcII ⁵⁷ Co!B₁₂ was then incubated with each monoclonal antibody to be tested (including 2-2, 4-7, 3-11), in the form of culture supernate or ascites, or with appropriate controls such as irrelevant culture supernatant, irrelevant ascites or mouse serum at 4° C. overnight. The cells were harvested and washed twice in Hank's balanced salt solution (HBSS), at between 1 and 1.5×10⁶ cells in 500 uL. These cells were added to the antibody/TcII ⁵⁷ Co!B₁₂ mixture along with 100 uL of 100 mM calcium and incubated for 1 hour at 37° C. One hundred uL of 100 nM EDTA was used in place of calcium to determine non-specific binding since TcII binding to the receptor is calcium dependent. Cellular uptake of ⁵⁷ Co!B₁₂ was determined by counting the radioactivity from ⁵⁷ Co in the cell pellets produced by centifuging the samples at 2000 RPM for 5 minutes in a Hermle centifuge. These results are reported in FIG. 6. A surprising result was that several clones also increased uptake. It is not clear at this time if the increase causes and/or results from an increase in proliferation, or if it indicates that cross-linking of TcII and thereby receptor causes increased internalization.

Example 11 Determination of Specificity for Holo- or Apo- TcII

Three of the clones which inhibited vitamin B₁₂ uptake (2-2, 3-11, 4-7) (FIG. 5), were then tested to determine their specificity for holo- versus apo- form of TcII using conventional immunoprecipitation techniques. Specifically, recombinant TcII purified by chromatography on carboxymethyl-Sephadex (Quadros et al., J. Biol. Chem., 261(33):15455-15460, 1986) to yield the apo-form of the carrier protein was radiolabeled with ¹²⁵ I (Amersham) as previously described in Quadros et al., Am. J. Physiol. 256:296-303, 1989. Holo-TcII was prepared from this material by incubating an aliquot at room temperature for 30 minutes with sufficient vitamin B₁₂ (Sigma) to saturate apo-TcII. Antibodies to be tested were captured on Sepharose beads conjugated with protein-A, washed in HBSS, incubated with either ¹²⁵ I-holo-TcII or ¹²⁵ I-apo-TcII, washed, and bound radioactivity determined on a gamma counter. A polyclonal rabbit antibody to TCII was used as a positive control.

As shown in FIG. 7, all three clones bound preferentially to holo-TcII. The results indicate that binding of B₁₂ to TcII leads to expression of a neodeterminant on the molecule. This determinant is related to the region of TcII that is recognized by the receptor, and that it may be responsible for the specificity of the receptor for holo-TcII.

Example 12 Purification of Antibodies

Growth blocking agents were produced by hybridoma clones 1-9, 3-9, 5-18, and 3-11 grown in DMEM 10% fetal bovine serum, 0.2% β-mercaptoethanol, and 2% 3T3 conditioned medium (a source of Interleukin 6) in 1 L glass roller bottles. The culture supernatant was collected and stored frozen prior to the commencement of this project. Thawed supernatant was filtered through a 0.22 μm filter to remove any bacteria or cell debris, then buffered with 1M Hepes, pH 7.2. Antibody was purified from this culture medium by affinity chromatography on sheep-anti-mouse immunoglobulin columns as follows:

Column and buffers were allowed to warm to room temperature. Phosphate-buffered saline (1×PBS) with 0.5% sodium azide was allowed to drain from the column. The column was pre-cycled with 200 mL PBS, then 200 mL 0.1M glycine, pH 2.5, to clear any contaminants, then re-equilibrated with 200 mL of PBS. The pH of the buffer running through the column at this point was checked with pH paper to be 7.0-8.0. 200 mL of culture medium was applied to the column, allowed to run through and collected as "drop thru". This drop thru was then reapplied to the column. The pH was checked at this stage to be approximately 7.4. 200 mL PBS was added to the column to wash through any unbound protein, and the first 20 mL was collected in a separate tube as "wash 1". The pH was checked here to be 7.0-8.0. The last of the buffer was aspirated through the column with a syringe. 8 mL of 0.1M glycine was added to the column and allowed to sit for 10 minutes. Eight 1 mL fractions were collected from the column, the pH was checked to be 2.5. The fractions were then neutralized with 35 μL of saturated tris buffer. Optical density readings of the elutes were taken at 280 nm to determine which ones had sufficient antibody to keep. Protein concentration was calculated in mg/mL using the equation:

    1.4 O.D.=1 mg/mL.

Elutes which gave O.D. readings above 0.12 were pooled and concentrated by high pressure filtration using a YM 10 43 mm membrane filter. PBS was washed through the filtration apparatus 3× to wash out any glycine/tris buffer and to resuspend the antibodies in a solution of neutral pH. Optical density readings at 280 nm were taken to obtain the final concentration. The solutions were filtered sterile with a 0.22 μm syringe filter and stored at 4° C.

Example 13 Determination of Purified Protein as Antibody

The purified protein samples were determined to be antibody by electrophoresis on SDS-PAGE gel, under both reducing and non-reducing conditions (to visualize both the entire antibody molecules and the heavy and light chains). SDS-PAGE mini-gels were prepared using Mini-PROTEAN II Dual Slab Cell from Bio-Rad Laboratories. Glass plates, spacers, combs, and casting stand gasket were cleaned with ethanol before use. The following procedure was used:

Gel sandwich was assembled ensuring that the plates and spacers were flush. A 6% acrylamide separating gel was prepared with 2 mL acrylamide, 5.44 mL distilled water, 2.5 mL 1.5M Tris-HCl, pH 8.8, 50 μL 10% APS and 10 μL Temed. 4.7 mL was pipetted between two of the gel plates. A 12% gel was prepared similarly, with the exception that 4 mL of acrylamide and 3.44 mL of distilled water were used. To ensure that no air bubbles formed, a layer of distilled water was pipetted above each gel. Both gels were allowed to polymerize for 20 minutes. Distilled water was removed by vacuum.

Stacking gel was prepared with 0.833 mL acrylamide/Bis, 2.9 mL distilled water, 1.25 mL 1.5M Tris-HCl, pH 6.8, 20 μL 10% APS, and 10 μL of Temed. The gel was pipetted between the gel sandwiches and a comb was immediately placed into each and allowed to polymerize for 30 minutes. Combs were removed and the sample lanes rinsed with distilled water. Gels were attached to the inner coiling core and GST running buffer (Glycine, SDS, and Tris) was added to the center chamber.

Samples of the four monoclonal antibodies, 1-9, 3-9, 5-18, and 3-11 were prepared at 2-3 mg/mL, with bromophenol blue for the non-reducing 6% gel, and with both bromophenol blue and 2% β-Mercaptoethanol for the 12% reducing gel. These samples and both high and low molecular weight markers were loaded onto the gel, 5 μL was added per lane. The inner cooling core was placed into the lower burffer chamber. The chamber was filled with 1× GST, and any air bubbles were removed from the bottom of the gel.

The chamber was then sealed with the lid and connected to the power supply. The voltage was set at 100 volts until the samples reached the running buffer, when the voltage was raised to 200 volts. After electrophoresis was complete, the gel sandwich was removed from the apparatus. The upper and lower gel plates were detached and the stacking gel was discarded. The running gel was removed from the plate by placing the gel under 1× Semi-Dry Transfer buffer. The gels were fixed and stained using a modified from of the silver staining procedure of J. H. Morrissey (Analytical Biochemistry, 117:307-310, 1981).

Example 14 Determination of Antibody Isotype

An ELISA sandwich assay was used to determine the isotype of each of the four monoclonal antibodies purified, as well as another potentially useful growth blocking antibody, 2-6. Antibody tested for 2-6 was not purified, culture supernatant was added directly to the ELISA wells.

100 μL of isotype-specific rat-anti-mouse capture antibody was added to each well of a flat-bottom 96 well Falcon polyvinyl ELISA plate at a concentration of 5 μg/mL (prepared in 1× PBS). Two rows were coated per isotype (IgG1, IgG2a, IgG2b, IgG3, IgM, kappa and lambda light chains). One row contained only PBS as a measure of the background signal. The ELISA plates were incubated at room temperature overnight in a sealed container lined with damp paper towels. The well contents were emptied by slapping the plates on a paper towel, and 100 μL of 1× PBS 0.5% milk powder was added to each well to block non-specific binding. This was incubated at room temperature for 1 hour.

The four purified monoclonal antibodies and the control antibody, 2E11, which is known to be IgG1 kappa, were prepared at 5 μg/mL in PBS/milk. The plates were washed three times in PBS/milk, then 100 μL of each antibody solution was added to each well of 2 columns of the ELISA plate, so that each antibody was tested against each isotype. This was incubated at room temperature for 1 hour. The wells were emptied and the plate washed as in step 3. 100 μL of rat-anti-mouse immunoglobulin which was labeled with horseradish peroxidase diluted 1:1000 in PBS/milk, was added to each well on the plate and incubated for 1 hour. The plate was again washed as in step 3 and then rinsed 3× with distilled water. 2,2' Azinobis (3-ethylbenzthiazoline sulfonic acid, or ABTS) substrate was prepared at 1 mg/mL in citrate buffer, pH 4.5, with 2 μL/mL freshly prepared 3% hydrogen peroxide. 100 μL of this solution was added to each well on the ELISA plate and allowed to stand at 37° C. for approximately 20 minutes. Once a color-change reaction was observed, the plate was read on Bio-Tek Microplate EL 309 ELISA Reader.

The isotypes of the purified antibodies are shown in Table 4.

                  TABLE 4                                                          ______________________________________                                         1-9                 1gG2a kappa                                                3-9                 1gG1 kappa                                                  5-18               1gG2a kappa                                                2-6                 1gG1 kappa                                                  3-11               1gG2a kappa                                                ______________________________________                                    

Example 15 Determination of Antibody Specificity for Transcobalamin II

A similar ELISA sandwich assay was used to determine whether the purified antibodies recognize TCII as was used for the isotyping experiment. In this procedure, the four purified monoclonal antibodies were mixed together at 10 μg/mL (2.5 μg/mL of each antibody) in PBS and 100 μL was added to each well. This was incubated overnight, then the plates were washed and blocked in PBS 0.5% milk. 100 μL 5× concentrated human serum or 5× concentrated fetal bovine serum was added to the first well of each row on the plates. The sera were then titrated (serially diluted) in PBS/milk across the plates: each step diluted the sera 2×. This was incubated for 1 hour, washed and blocked, then purified anti-TCII antibodies which had been labeled with biotin were added, this time singularly, to each well of two rows. This was incubated for 1 hour, washed and blocked, then 50 μL of horseradish peroxidase-labeled streptavidin, diluted 1:2000 in PBS/milk, was added to each well. This was incubated for 2 hours, washed/blocked, substrate solution was added as per the isotyping protocol, and read on the ELISA reader. Once results were obtained from this experiment, it was repeated with normal concentration of human serum, mouse serum, rhesus monkey serum, and recombinant TCII. Mouse serum was of limited availability, so only 50 μL was added to the first well of ELISA plate instead of 100 μL. Results are shown in FIG. 8.

Antibody 5-18 was found to perform poorly as a capture antibody despite showing reasonable activity as a detector with 3-11 and 3-9. However, it showed no response in combination with 1-9, suggesting that both monoclonal antibodies may recognize the same epitope. The remaining combinations of monoclonal antibodies produced responses, which suggests that 3-11 and 3-9 see independent epitopes.

While the present invention has been disclosed and described with reference to specific embodiments, it will be understood by those skilled in the art that various changes or modifications in form and detail may be made without departing from the spirit and scope of this invention. 

I claim:
 1. A method for inhibiting cell division of a target cell in a warm-blooded animal, comprising administering to the animal a monoclonal anti-receptor antibody to a vitamin B₁₂ /transcobalamin II receptor on the surface of the target cell, said monoclonal antibody being capable of competitively antagonizing or modulating the receptor to prevent or inhibit cellular uptake of vitamin B₁₂ by the target cell.
 2. A method for preventing or inhibiting cellular uptake of vitamin B₁₂ in a warm-blooded animal, comprising administering to the animal monoclonal anti-receptor antibody to a vitamin B₁₂ /transcobalamin II receptor on the surface of the cell, said monoclonal antibody being capable of competitively antagonizing or modulating the receptor to prevent or inhibit the cellular uptake of vitamin B₁₂.
 3. The method of claim 1 wherein said cell is an activated lymphoid cell.
 4. The method of claim 1 wherein said cell is an activated T cell.
 5. The method of claim 1 wherein said cell is a tumor cell.
 6. The method of claim 1 wherein said cell is a bone marrow stem cell.
 7. The method of claim 1 wherein said cell is a proliferating fibroblast cell.
 8. The method of claim 1 wherein said cell is selected from the group consisting of a proliferating epithelium and epidermal cell.
 9. The method of claim 2 wherein said cell is a neoplastic cell.
 10. The method of claim 2 wherein said cell is an activated lymphoid cell.
 11. The method of claim 2 wherein said cell is an activated T cell.
 12. The method of claim 2 wherein said cell is a tumor cell.
 13. The method of claim 2 wherein said cell is a bone marrow stem cell.
 14. The method of claim 2 wherein said cell is a proliferating fibroblast cell.
 15. The method of claim 2 wherein said cell is selected from the group consisting of a proliferating epithelium and epidermal cell.
 16. A method of inhibiting cell division in a warm blooded animal comprising administering to a warm blooded animal a therapeutically effective amount of a monoclonal anti-receptor antibody to a vitamin B₁₂ /transcobalamin II receptor on the surface of the cell, said monoclonal antibody being capable of competitively antagonizing or modulating the binding site to prevent or inhibit the uptake of vitamin B₁₂ by TcII.
 17. A method of preventing or inhibiting cellular uptake of vitamin B₁₂, comprising administering to an animal a therapeutically effective mount of a monoclonal anti-receptor antibody to a vitamin B₁₂ /transcobalamin II receptor on the surface of the cell, said monoclonal antibody being capable of competitively antagonizing or modulating the binding site to prevent or inhibit the uptake of vitamin B₁₂ by TcII.
 18. A method of preventing or inhibiting cellular uptake of vitamin B₁₂, comprising administering to a biological preparation an effective amount of a monoclonal anti-receptor antibody to a vitamin B₁₂ /transcobalamin II receptor on the surface of the cell, said monoclonal antibody being capable of competitively antagonizing or modulating the binding site to prevent or inhibit the uptake of vitamin B₁₂ by TcII.
 19. A method of inhibiting cell division in a warm blooded animal comprising administering to a warm blooded animal a therapeutically effective amount of a monoclonal antibody to a binding site on a TcII/B₁₂ complex, said monoclonal antibody being capable of competitively antagonizing or modulating said binding site to prevent or inhibit the binding of said TcII/B₁₂ complex to the cell surface.
 20. A method of preventing or inhibiting cellular uptake of vitamin B₁₂ comprising administering to an animal an effective amount of a monoclonal antibody to a binding site on a TcII/B₁₂ complex, said monoclonal antibody being capable of competitively antagonizing or modulating said binding site to prevent or inhibit the binding of said TcII/B₁₂ complex to the cell surface.
 21. A method of inhibiting cellular uptake of vitamin B₁₂ comprising administering to a biological preparation an effective amount of a monoclonal antibody to a binding site on a TcII/B₁₂ complex, said monoclonal antibody being capable of competitively antagonizing or modulating said binding site to prevent or inhibit the binding of said TcII/B₁₂ complex to the cell surface. 